In the case of Judaism, Israel makes Orthodox conversion more useful since it doesn't accept you as a real Jew if you are a convert to a more weak tea version of Judaism. People who convert are usually stronger believers, so they would convert to the more undiluted version of the religion anyway.
On the other hand, 'cultural' Jews are more likely to marry non-Jews, and absorb them into Judaism that way. And I suppose this leads to cultural Jews leaving Judaism too. I think I read somewhere that the descendants of all the founders of Reform Judaism ended up outside Judaism.
> People who convert are usually stronger believers, so they would convert to the more undiluted version of the religion anyway.
That doesn't follow; converts are very often quite passionate about the beliefs of the group they convert to, and it's distinction form others, but that doesn't mean that they necessarily prefer the version that is seen as most pure by outsiders.
Israel will accept you for making aliyah with any conversion (or none, if you have even a small amount of Jewish blood). Being a "real Jew" in the eyes of Israel may have some cachet for someone... but I don't know anybody who made a decision about which movement to convert in on that basis. I also doubt seriously that the Orthodox movement experiences more conversion than the other movements. It's smaller than either the Reform or Conservative movements.
For making aliyah, you do not have to have an Orthodox conversion. This issue really only comes up for marriage. And of course, Israel has (in their typical fashion) chosen the solution guaranteed to annoy the most people.
On the other hand, 'cultural' Jews are more likely to marry non-Jews, and absorb them into Judaism that way. And I suppose this leads to cultural Jews leaving Judaism too. I think I read somewhere that the descendants of all the founders of Reform Judaism ended up outside Judaism.